The invention relates to ultrasonic sector scanners, and motors, control systems, cover assemblies and nose pieces therefore. Such devices are used, for example, in medical diagnostics.
In ultrasonic "A-scanners", an ultrasonic transducer generates an acoustic pressure signal and projects the signal in a straight line through a body. The projected signal is scattered along its path of propagation, and as a result generates an echo acoustic pressure signal. The echo pressure signal contains information regarding the nature of the body along the path of propagation. The ultrasonic transducer receives the echo pressure signal and converts it into an electrical signal.
A two-dimensional image of a cross-section through the body is obtained in an ultrasonic "A-scanner", by pivoting the ultrasonic transducer through a selected angular range in order to scan the cross-sectional layer. Each electrical echo signal then represents an image of a radial line in the layer; all the electrical echo signals together represent an image of a pie-shaped cross-sectional layer of the body. By suitable processing of the electrical echo signals and an accurate measure of the pivot angle of the transducer, an image of the layer can be displayed on, for example, a cathode ray tube screen.
In practice, the ultrasonic transducer is not pivoted only one time through the selected angular range. In practice, the transducer is oscillated back and forth many times. Each repeated oscillation of the transducer produces a new image of the cross-sectional layer of the body, thus resulting in real-time imaging of the layer.
The motor used to oscillate the ultrasonic transducer must supply torque (i) to periodically reverse the direction of rotation of the transducer, (ii) to overcome frictional losses, for example due to the fiscous drag of the liquid in which the transducer is typically immersed, and (iii) to cause the transducer to track a reference signal when a servo-control system is utilized. The torque required to overcome frictional losses is usually relatively small. Moreover, preferably the angular velocity of the transducer is constant throughout the scan thereby requiring a small tracking torque. Accordingly, typically 75%-90% of the torque requirement of the scanning device arises from the direction-reversal requirement.
As mentioned above, the ultrasonic transducer is typically immersed in a liquid coupling medium. In order to contain this liquid in the ultrasonic sector scanner, the ultrasonic transducer and motor are covered with either a rigid dome or with a dome-shaped flexible membrane. When a membrane is used, the membrane is sealed to the housing of the sector scanner with an adhesive to prevent leakage of the coupling liquid. When replacement of the flexible membrane becomes necessary, one must first remove the old membrane, then remove the old adhesive, then reapply new adhesive and affix the new membrane. As a result, replacement of the flexible membrane is a delicate and time consuming process.
Moreover, in existing ultrasonic sector scanners, a rigid nose piece partially covers the transducer/motor assembly. The nose piece is provided to protect this assembly from damage due to direct contact with the flexible membrane, when the membrane is pressed against a patient being examined. An opening is provided in the nose piece for transmission of ultrasonic waves therethrough. The flexible membrane is then stretched over the nose piece to seal the housing.